Most trial lesson students don't go on to further their flying and hence aren't really interested in the pre-flight inspection so the instructor would have done that first in order not to waste your time. Unless he knew (or you had asked) that you wanted to go through the check, then it was perfectly reasonable that he did it before you arrived, just as he would have checked the weather, NOTAMs, etc.
If this local school offers a fair price for training, is professional and you have confidence in them, then do your PPL there! It's only at the CPL stage (and subsequent) that employers do not want to see too many schools on a CV (and even then, that's debatable).
Cheers
Whirls